 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui;

 import org.eclipse.core.expressions.EvaluationResult;
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.ExpressionInfo;
 import org.eclipse.core.expressions.IEvaluationContext;
 import org.eclipse.swt.widgets.Shell;

 /**
  * <p>
  * An expression that checks the active shell variable. The variable name is
  * <code>ISources.ACTIVE_SHELL_NAME</code> and falls back to
  * <code>ISources.ACTIVE_WORKBENCH_WINDOW</code>. That is, if the active
  * shell doesn't match, then it will be allowed to match the active workbench
  * window.
  * </p>
  *
  * @since 3.1
  */
 public final class ActiveShellExpression extends Expression {

     /**
      * The seed for the hash code for all schemes.
      */
     private static final int HASH_INITIAL = ActiveShellExpression.class
             .getName().hashCode();

     /**
      * The sources value to use with this expression.
      */
     public static final int SOURCES = ISources.ACTIVE_SHELL
             | ISources.ACTIVE_WORKBENCH_WINDOW;

     /**
      * The shell that must be active for this expression to evaluate to
      * <code>true</code>. If this value is <code>null</code>, then any
      * shell may be active.
      */
     private final Shell activeShell;

     /**
      * Constructs a new instance of <code>ActiveShellExpression</code>
      *
      * @param activeShell
      * The shell to match with the active shell; <code>null</code>
      * if it will match any active shell.
      */
     public ActiveShellExpression(final Shell activeShell) {
         this.activeShell = activeShell;
     }

     /**
      * Expression information for this expression. Namely active shell and
      * active workbench window name.
      *
      * @since 3.2
      */
     public final void collectExpressionInfo(final ExpressionInfo info) {
         info.addVariableNameAccess(ISources.ACTIVE_SHELL_NAME);
         info.addVariableNameAccess(ISources.ACTIVE_WORKBENCH_WINDOW_NAME);
     }

     protected final int computeHashCode() {
         return HASH_INITIAL * HASH_FACTOR + hashCode(activeShell);
     }

     public final boolean equals(final Object object) {
         if (object instanceof ActiveShellExpression) {
             final ActiveShellExpression that = (ActiveShellExpression) object;
             return equals(this.activeShell, that.activeShell);
         }

         return false;
     }

     /**
      * Evaluates this expression. If the active shell defined by the context
      * matches the shell from this expression, then this evaluates to
      * <code>EvaluationResult.TRUE</code>. Similarly, if the active workbench
      * window shell defined by the context matches the shell from this
      * expression, then this evaluates to <code>EvaluationResult.TRUE</code>.
      *
      * @param context
      * The context from which the current state is determined; must
      * not be <code>null</code>.
      * @return <code>EvaluationResult.TRUE</code> if the shell is active;
      * <code>EvaluationResult.FALSE</code> otherwise.
      */
     public final EvaluationResult evaluate(final IEvaluationContext context) {
         if (activeShell != null) {
             Object value = context.getVariable(ISources.ACTIVE_SHELL_NAME);
             if (!activeShell.equals(value)) {
                 value = context
                         .getVariable(ISources.ACTIVE_WORKBENCH_WINDOW_SHELL_NAME);
                 if (!activeShell.equals(value)) {
                     return EvaluationResult.FALSE;
                 }
             }
         }

         return EvaluationResult.TRUE;
     }

     public final String toString() {
         final StringBuffer buffer = new StringBuffer ();
         buffer.append("ActiveShellExpression("); //$NON-NLS-1$
 buffer.append(activeShell);
         buffer.append(')');
         return buffer.toString();
     }
 }

